Biomechanical evaluation of cervical double-door laminoplasty using hydroxyapatite spacer.

STUDY DESIGN: In vitro three-dimensional kinematic changes after double-door cervical laminoplasty, with and without spacer, and laminectomy were studied in a human cadaveric model.

OBJECTIVES: To evaluate the effects of multilevel double-door laminoplasty and laminectomy as compared with the intact and to assess the influence of the spinous process spacer on the stability of the cervical spine.

SUMMARY OF BACKGROUND DATA: Double-door type cervical laminoplasty has been widely used in the treatment of multisegmental stenotic conditions. However, its biomechanical advantages over laminectomy remain controversial. Also, the biomechanical effects of spacers between the split laminae have not been investigated.

METHODS: Using fresh cadaveric C2-T1 specimens, sequential injuries were created in the following order: intact, double-door laminoplasty (C3-C6) with insertion of hydroxyapatite spacers, laminoplasty without spacer, and laminectomy. Motions of each vertebra in each injury status were measured in six loading modes: flexion, extension, right and left lateral bending, and right and left axial rotation.RESULTS Cervical laminectomy showed significant increase in motion compared with intact control in flexion [25% (P < 0.001)], extension [19% (P < 0.05)], and axial rotation [24% (P < 0.001)] at maximum load. Double-door laminoplasty with hydroxyapatite spacer indicated no significant difference in motion in all loading modes compared with intact. Laminoplasty without spacer showed intermediate values between laminoplasty with spacer and laminectomy in all loading modes. Initial slack of each injury status showed trends similar to that of maximum load, although mean percent changes of laminectomy and laminoplasty without spacer were greater than that of maximum load.

CONCLUSIONS: Double-door laminoplasty with hydroxyapatite spacer appears to restore the motion of the decompressed segment back to its intact state in all loading modes. The use of HA spacers well contributes to maintaining the total stiffness of cervical spine. In contrast, laminectomy seems to have potential leading postoperative deformity or instability.